The nephrotic syndrome, characterized by edema and large amounts of protein in the urine, is a relatively common disorder of the kidney that has many potential causes, including membranous nephropathy (MN), focal and segmental glomerulosclerosis, minimal change disease, diabetic nephropathy, membranoproliferative glomerulonephritis, as well as other causes. Although there are non-specific treatments that ameliorate some of the signs and symptoms of the nephrotic condition, specific knowledge of the underlying disease is usually necessary to guide definitive treatment. When a patient with the nephrotic syndrome is initially evaluated as an outpatient or in the hospital, a panel of blood tests is usually ordered by the physician to look for potential causes that are detectable by serology (for example, the presence of anti-nuclear antibodies (ANA) and/or anti-double stranded DNA antibodies in the context of typical findings in the urinary sediment would suggest lupus nephritis). There is currently no serologic test to identify MN, and diagnosis relies exclusively on kidney biopsy, an invasive procedure requiring overnight hospitalization in many institutions and one that can be complicated by major internal bleeding. MN can be caused by a number of secondary factors, such as systemic lupus erythematosus, hepatitis B, or syphilis, and blood tests are routinely sent to look for these causes (ANA, anti-hepatitis B antigens, rapid plasma reagin (RPR), respectively). However, in the United States, MN is more often primary, or idiopathic, in origin and as mentioned above, no blood test for this form currently exists. Therefore, there is a need to identify the underlying cause of MN and develop a simple, non-invasive test to diagnose MN and follow the response to treatment.